Efforts in the RS virus genetics program were redirected to concentrate on the molecular characterization of the viral genome and its products. A cDNA library of RS virus mRNA (from infected cells) was constructed in E. coli. using a plasmid vector and oligo dG/dC tailing. The first cDNA was transcribed by a technique that avoided the use of S1 nuclease and self priming. Recombinant plasmids containing viral sequences for at least 4 viral proteins were identified by (a) selection of plasmid DNAs that reacted with viral specific labeled mRNA, (b) hybrid selection of mRNA by recombinant cDNAs and translation of such mRNAs and/or (c) hybrid arrested translation of viral mRNAs by recombinant plasmids. The cloned viral DNAs in these plasmids are currently being sequenced to establish the reading frame of the various viral polypeptides.